1. Field of the Invention
The invention pertains to the field of blade tensioners. More particularly, the invention pertains to a blade tensioner equipped with a blade shoe having a chain sliding face and numerous leaf spring-shaped blade springs for applying a spring force to this blade shoe.
2. Description of Related Art
Blade tensioners have been used in the past to apply tension to chains. An example of a blade tensioner is shown in FIG. 10. The conventional blade tensioner (100) includes a blade shoe (101) made of resin having a curved chain sliding face (101a) and numerous blade springs (102) preferably made of metallic material. The blade springs (102) are arranged in layers on the opposite side of blade shoe (101) from chain sliding face (101a), and provide spring force to blade shoe (101). The ends of each spring-shaped blade spring (102) are inserted in the indented portions (111) and (113) which are formed in the distal portion (110) and proximal portion (112) of blade shoe (101), respectively.
A bracket (120) is provided for mounting blade tensioner (100) in an engine. Holes (121) and (122) are formed in bracket (120), and mounting bolts are inserted into these holes (121) and (122). Sliding face (125) contacts the distal portion of blade shoe (101) and permits sliding. Slide face (125) is formed on the distal portion of bracket (120). One end of pin (130), which supports the proximal portion (112) of blade shoe (101) so that it may move in either direction, is secured in the center of bracket (120).
When the chain is operating, the chain continues to slide and run on sliding face (101a) of blade shoe (101). The pushing load accompanying the change in the shape of blade shoe (101) and blade springs (102) is applied to the chain so that a constant tension is maintained in the chain. Likewise, the oscillation due to the clattering of the chain and variations in tension are transmitted to the respective blade springs (102) in blade shoe (101) by virtue of blade shoe (101). Each blade spring (102) repeatedly deforms elastically and returns, and the oscillation of the chain is dampened by adjacent blade springs (102) sliding together.
Referring also to FIG. 11, there is ample variation in the curvature and length in blade springs as products. As a result, when numerous blade springs are layered and installed in blade shoes, variation occurs in the contact position of each blade spring (contact point) C, Cxe2x80x2, state of contact and gap T. Consequently, variation in the damping coefficient of the blade springs overall occurs and the problem of inconsistency of damping performance of the blade tensioner can arise.
Therefore, there is a need in the art for a blade tensioner that stabilizes damping performance.
This invention provides a blade tensioner comprised of a blade shoe having a chain slide face, a plurality of blade springs for applying spring force to the blade shoe, and a spacer member interposed between the adjacent blade springs. Each of the blade springs is preferably in the shape of a leaf spring. The blade springs are positioned and layered on the opposite side of the blade shoe from the chain slide face. The spacer member preferably contacts the corresponding blade spring at two contact points apart from each other at a uniform distance. In the blade tensioner of this invention, the blade spring contacts the spacer member at a constant span, which causes the damping coefficient of the whole blade spring to be constant and also allows the damping performance of the blade tensioner to be stable.